Ocean ventilation rates describe the time since a deep water mass last was in contact with the atmosphere. Understanding and constraining this time in the modern and past ocean is of major importance, as the formation of deep waters at high latitudes involves carbon exchange with the atmosphere thereby exerting a key influence on climate. The research proposed here will develop a novel method for determining past ocean ventilation rates: paired neodymium (Nd) isotope and radiocarbon (14C) measurements from deep-sea corals. Radiocarbon measurements in U-series dated deep-sea corals have been successfully used to constrain the radiocarbon content of the deep ocean during the last deglaciation, but without knowing the mixing ratio of different water masses we cannot convert radiocarbon data to ocean ventilation rates. Different water masses in the ocean are characterized by distinct Nd isotopic compositions, whose values are ultimately controlled by regional continental weathering, erosion, and particle-seawater interaction. Therefore this proxy will be used as a quasi-conservative water-mass-mixing tracer. In this project, the PIs will evaluate whether different species of modern deep-sea corals record the Nd isotopic composition of ambient deep water, and whether fossil corals preserve this Nd isotope signature. These data have the potential to produce a new method for accurately determining past ocean ventilation rates. The results of this multiproxy approach have the potential to provide links between ocean ventilation, the carbon cycle, and climate change for researchers studying a broad array of questions in the fields of carbonate chemistry, geochemical cycling in the ocean, the global carbon cycle and paleoceanography. Undergraduate students on summer internships will be introduced to the fields of paleoceanography and geochemistry through discrete projects involving analytical measurements in modern and fossil deep-sea corals.
